docs: def get_bundle_for_cn(cn, relation_name=None):
      """Extract certificates for the given cn.
  
      :param cn: str Canonical Name on certificate.
      :param relation_name: str Relation to check for certificates down.
      :returns: Dictionary of certificate data,
      :rtype: dict.
      """
      entries = get_requests_for_local_unit(relation_name)
      cert_bundle = {}
      for entry in entries:
          for _cn, bundle in entry['certs'].items():
              if _cn == cn:
                  cert_bundle = {
                      'cert': bundle['cert'],
                      'key': bundle['key'],
                      'chain': entry['chain'],
                      'ca': entry['ca']}
                  break
          if cert_bundle:
              break
      return cert_bundle